One automatic spark timing advance system senses engine speed, such as by monitoring either the negative bias voltage applied to bias controlled rectifier circuitry used to control the spark angle or the high speed alternator winding output, for operating an auxiliary controlled rectifier to conduct opposite polarity pulses from the alternator to trigger the controlled rectifier circuitry to provide an advanced spark angle at higher speeds, such as provided in the application by Arthur O. Fitzner and entitled "Ignition System for Multiple Cylinder Internal Combustion Engines Having Automatic Spark Advance", which issued on Apr. 1, 1975 to U.S. Pat. No. 3,874,349 and is assigned to a common assignee herewith.
The U.S. Pat. No. 3,898,894, which issued on Aug. 12, 1975 and is entitled "Engine Ignition Timing Control", discloses a system for controlling ignition spark timing by modulating the pulse width of a pulse signal to provide ignition timing throughout the varying operating conditions of the engine.
Another system employs a "bucket" type tachometer circuit connected to a pilot trigger capacitor to receive a pulse rate related charging signal to operate a field-effect transistor operating to vary the resistance across a timing stabilizing threshold bias capacitor to reduce the bias voltage for lowering the triggering threshold to automatically advance the spark at idle speeds, such as provided in the application by Arthur O. Fitzner and entitled "Ignition System with Idle Speed Governor Apparatus", which issued on Jan. 4, 1977 to U.S. Pat. No. 4,111,174 and is assigned to a common assignee herewith.
Another prior spark timing advance senses a plurality of pulses provided by the alternator high speed winding during each cycle of the ignition system operation to vary the negative bias voltage which biases the controlled rectifier circuitry to provide an advanced spark angle limited to low speeds and wherein the high speed winding is lightly loaded and provides essentially undistorted signals at such low speeds, such as provided in the application by Arthur O. Fitzner and entitled "Low Speed Limiter Unit for Internal Combustion Engine Ignition Systems", which issued on Jan. 13, 1981 to U.S. Pat. No. 4,244,336 and assigned to a common assignee herewith.